The present invention relates to a reclining device adapted for variable setting of the tilt angle of a seat back of an automobile seat, for example.
There are various types of reclining devices. A hinge device described in Jpn. Pat. Appln. KOKOKU Publication No. 3-52965 is one such known device. In this device, an internal gear and a latch member are provided on a stationary plate and a movable plate, respectively, and a seat back is locked by causing the latch member to engage the internal gear. According to this prior art, an operating lever is pivotally mounted in a position separate from a shaft, the motion of the lever is transmitted to a cam by means of a link, and the latch member is actuated by means of the cam.
If the axis of rotation of the operating lever is deviated from the center of the shaft, as in the prior art device (Jpn. Pat. Appln. KOKOKU Publication No. 3-52965), the motion of the lever must inevitably be transmitted to the cam by means of an intermediate member such as the link. Therefore, the path of transmission of force from the operating lever to the latch member is subject to a substantial load loss or stroke loss.
Accordingly, an internal-gear reclining device 100, such as the one shown in FIG. 13, has been proposed in order to enable the operating lever to transmit operating force thereon to the cam member without any loss. This device 100 comprises a base plate 101, an operating lever 103 rotatable around a shaft 102 fixed to the plate 101, and a movable arm 105 rotatably supported on the shaft 102 and having an internal gear 104. The device 100 further comprises a latch member 111, a cam member 113, a coupling member 114, etc. The latch member 111 is interposed between the base plate 101 and the movable arm 105, and is movable along a groove 110 in the plate 101. The cam member 113 is fitted in a recess 112 in the base plate 101, and is rotatable around the shaft 102. The coupling member 114 serves to transmit the rotary motion of the operating lever 103 to the cam member 113.
In the reclining device 100, as shown in FIG. 14, a gear portion 111a of the latch member 111 is pressed against the internal gear 104 by the cam member 113 when the operating lever 103 is lowered. As the internal gear 104 engages the gear portion 111a, the movable arm 105 is fixed to the base plate 101, that is, the seat back is fixed (or locked). When the operating lever 103 is pulled up, it rotates around the shaft 102, and at the same time, the cam member 113 rotates around the shaft 102. Thereupon, the cam member 113 shifts its position so that the latch member 111 is disengaged from the internal gear 104. Thus, the movable arm 105 is released from the latch member 111 or unlocked so that it can rotate relatively to the base plate 101.
The reclining device 100 is provided on one side of a seat. In the case of a bilateral-locking recliner, a second reclining device 100' that resembles the reclining device 100 in construction is located on the other side of the seat. The paired reclining devices 100 and 100' are designed so that their respective cam members 113 (only one of which is shown) are linked together by means of a coupling rod 117.
As shown in FIG. 15, the conventional internal-gear reclining device 100 is provided with an offset portion, which includes the groove 110 for holding the left-hand half of the latch member 111 and a recess 112 for holding the left-hand half of the cam member 113. The groove 110 and the recess 112 are obtained by stamping out parts of the base plate 101 to the left-hand side by pressing. On the other hand, a recess 120 for holding the respective right-hand halves of the members 111 and 113 are formed by stamping out part of the movable arm 105. The internal gear 104 is formed on an end of the recess 120. Since the latch member 111 is stamped out of its material by fine blanking, the gear portion 111a extends across the overall thickness of the latch member 111.
In the case where the latch member 111 and the cam member 113 are held between the base plate 101 and the movable arm 105, the thicknesses T1 and T2 of the members 111 and 113 must be approximated to a distance T3 between the respective inner surfaces of the groove 110 and the recess 120, in order to lessen excessive play in the thickness direction of the members 111 and 113. In a mating region A between the internal gear 104 and the gear portion 111a of the latch member 111, therefore, the gear 104 and the portion 111a engage each other for only half the gear thickness of the portion 111a. In other words, about half the thickness of each of the members 111 and 113 is a superfluous thickness, for which the reclining device becomes thicker and heavier in weight, and its material cost is higher.
In the conventional internal-gear reclining device 100, moreover, the pressed portions, such as the groove 110 and the recess 112 of the base plate 101, are large-sized and complicated in shape. Accordingly, the base plate 101 can be molded only by fine blanking, which requires use of more expensive dies than in normal pressing and entails higher costs. If the latch member 111 is too thick, on the other hand, there is a problem that the gear portion 111a, a small module, cannot be stamped out.
Further, load may be concentrated on the mating region A between the internal gear 104 and the latch member 111 when a torque Q (shown in FIG. 14) is applied to the region A in case of a vehicle crash or the like. In some cases, therefore, the mating region A may be lowered in strength.
If a force of inertia from the body of an occupant of the vehicle is applied to the seat back in case of a crash, an inward torsional load, as well as the aforesaid torque Q, is generated in the reclining device 100. This torsional load acts in the direction to separate the base plate 101 and the arm 105 from each other. When the plate 101 and the arm 105 are separated, the depth of engagement between the internal gear 104 and the latch member 111 is reduced, so that the strength of the mating region A is lowered inevitably.
Conventionally, therefore, a bracket 130 is used to prevent the separation between the base plate 101 and the arm 105, as shown in FIG. 16. If this bracket 130 is additionally used in the reclining device 100, however, the weight of the device, as well as the number of its components, increases.
In the conventional reclining device 100 shown in FIG. 17, the groove 110 for holding the latch member 111 includes two parallel surfaces 110a and 110b for guiding the member 111 in sliding motion. In order to enable the member 111 to slide smoothly along the surfaces 110a and 110b, a clearance (gap) G must be defined by the member 111 and the surfaces 110a and 110b. This clearance G is equal to the difference between a width .omega.2 of the latch member 111 and a distance 107 1 between the two surfaces 110a and 110b. In consideration of the dimensional tolerances of the latch member 111 and the base plate 101 and the like, the clearance G should be made considerably large. It has been found, however, that this clearance G may cause excessive play between the plate 101 and the member 111 and make the seat back shaky.